Adjustment of sensory stimulation intensity to enhance sleep slow wave activity

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application Serial No. PCT/IB2014/060344, filed on Apr. 1, 2014, which claims the benefit of U.S. application Ser. No. 61/812,908, filed on Apr. 17, 2013. These applications are hereby incorporated by reference herein.

BACKGROUND

1. Field

The present disclosure pertains to a system and method for managing a current sleep session of a subject. One or more sensory stimulators incrementally increase the intensity of sensory stimuli provided to a subject during periods of slow wave sleep.

2. Description of the Related Art

Systems for monitoring sleep are known. Sensory stimulation during sleep is known. Sensory stimulation during sleep is often applied continuously at intervals and/or intensities that do not correspond to sleeping patterns of a subject. The present disclosure overcomes deficiencies in prior art systems.

SUMMARY

Accordingly, one or more aspects of the present disclosure relate to a system configured to manage a current sleep session of a subject. The system comprises one or more sensory stimulators, one or more sensors, and one or more processors. The one or more sensory stimulators are configured to provide sensory stimuli to the subject. The one or more sensors are configured to generate output signals conveying information related to a current sleep stage of the subject during the current sleep session. The one or more processors are configured to execute computer program modules. The computer program modules comprise a sleep stage module, a slow wave sleep timing module, a control module, an effectiveness module, and an adjustment module. The sleep stage module is configured to determine the current sleep stage of the subject based on the output signals. The sleep stage module is configured to determine whether the subject is presently in slow wave sleep. The slow wave sleep timing module is configured to determine individual time periods of slow wave sleep during the current sleep session based on the sleep stage determinations by the sleep stage module. The control module is configured to control the one or more sensory stimulators to provide the sensory stimuli to the subject during the individual time periods of slow wave sleep. The control module is configured to control the one or more sensory stimulators to provide the sensory stimuli at a first intensity level during a first individual time period of slow wave sleep. The effectiveness module is configured to determine an effectiveness of the provided sensory stimuli. The effectiveness is related to an increase in slow wave activity (SWA) caused by the sensory stimuli. In some embodiments, SWA corresponds to the power of an electroencephalogram signal in the 0.5-4.0 Hz band. In some embodiments, this band is set to 0.5-4.5 Hz. The effectiveness is determined based on the output signals. The effectiveness module is configured to determine a first effectiveness of the sensory stimuli provided at the first intensity level during the first individual time period. The adjustment module is configured to cause the one or more sensory stimulators to increase the intensity of the provided sensory stimuli based on the determined effectiveness. The intensity of the provided sensory stimuli is increased to a second intensity level based on the first effectiveness. The effectiveness module and the adjustment module are configured to repeat the effectiveness determination and the intensity increase one or more times during the individual time periods of slow wave sleep until expiration of the individual time periods such that the effectiveness module determines a second effectiveness of the sensory stimuli provided at the second intensity level during the first individual time period of slow wave sleep and the adjustment module causes the one or more sensory stimulators to increase the intensity of the provided sensory stimuli to a third intensity level. In some embodiments, the sleep stage module is configured to determine one or more arousal levels of the subject during the individual time periods of slow wave sleep. The adjustment module is configured to cause the sensory stimulators to decrease the intensity of, and/or cease providing, the sensory stimulation to the subject during a given period of slow wave sleep responsive to an arousal level determined by the sleep stage module breaching an arousal level threshold during the given period of slow wave sleep.

Yet another aspect of the present disclosure relates to a method for managing a current sleep session of a subject with a management system. The system comprises one or more sensory stimulators, one or more sensors, and one or more processors configured to execute computer program modules. The computer program modules comprise a sleep stage module, a slow wave sleep timing module, a control module, an effectiveness module, and an adjustment module. The method comprises generating, with the one or more sensors, output signals conveying information related to a current sleep stage of the subject during the current sleep session; determining, with the sleep stage module, the current sleep stage of the subject based on the output signals; determining, with the sleep stage module, whether the subject is presently in slow wave sleep based on the sleep stage determinations; determining, with the slow wave sleep timing module, individual time periods of slow wave sleep during the current sleep session based on the sleep stage determinations; controlling, with the control module, the one or more sensory stimulators to provide sensory stimuli to the subject during the individual time periods of slow wave sleep, the controlling including controlling the one or more sensory stimulators to provide the sensory stimuli at a first intensity level during a first individual time period of slow wave sleep; determining, with the effectiveness module, an effectiveness of the provided sensory stimuli, the effectiveness being related to an increase in slow wave activity caused by the sensory stimuli, the effectiveness being determined based on the output signals such that a first effectiveness of the sensory stimuli provided at the first intensity level during the first individual time period is determined; causing, with the adjustment module, the one or more sensory stimulators to increase the intensity of the provided sensory stimuli based on the determined effectiveness such that the intensity of the provided sensory stimuli is increased to a second intensity level based on the first effectiveness; and repeating, with the effectiveness module and the adjustment module, the effectiveness determination and the intensity increase one or more times during the individual time periods of slow wave sleep until expiration of the individual time periods such that a second effectiveness of the sensory stimuli provided at the second intensity level during the first individual time period of slow wave sleep is determined and the one or more sensory stimulators are caused to increase the intensity of the provided sensory stimuli to a third intensity level. In some embodiments, the method further comprises determining, with the sleep stage module, one or more arousal levels of the subject during the individual time periods of slow wave sleep, and causing, with the adjustment module, the sensory stimulators to decrease the intensity of and/or cease providing, the sensory stimulation to the subject during a given period of slow wave sleep responsive to an arousal level breaching an arousal level threshold during the given period of slow wave sleep.

Still another aspect of present disclosure relates to a system configured to manage a current sleep session of a subject. The system comprises means for providing sensory stimuli to the subject, means for generating output signals conveying information related to a current sleep stage of the subject during the current sleep session, and means for executing computer program modules. The computer program modules comprise means for determining the current sleep stage of the subject based on the output signals, the means for determining the current sleep stage configured to determine whether the subject is presently in slow wave sleep; means for determining individual time periods of slow wave sleep during the current sleep session based on the sleep stage determinations; means for controlling the means for providing sensory stimuli to provide the sensory stimuli to the subject during the individual time periods of slow wave sleep, the means for controlling configured to control the means for providing sensory stimuli to provide the sensory stimuli at a first intensity level during a first individual time period of slow wave sleep; means for determining an effectiveness of the provided sensory stimuli, the effectiveness being related to an increase in slow wave activity caused by the sensory stimuli, the effectiveness being determined based on the output signals, the means for determining an effectiveness configured to determine a first effectiveness of the sensory stimuli provided at the first intensity level during the first individual time period; and means for causing the means for providing sensory stimuli to increase the intensity of the provided sensory stimuli based on the determined effectiveness such that the intensity of the provided sensory stimuli is increased to a second intensity level based on the first effectiveness, wherein the means for determining an effectiveness and the means for causing are configured to repeat the effectiveness determination and the intensity increase one or more times during the individual time periods of slow wave sleep until expiration of the individual time periods such that the means for determining an effectiveness determines a second effectiveness of the sensory stimuli provided at the second intensity level during the first individual time period of slow wave sleep and the means for causing causes the means for providing sensory stimuli to increase the intensity of the provided sensory stimuli to a third intensity level. In some embodiments, the means for determining the current sleep stage is configured to determine one or more arousal levels of the subject during the individual time periods of slow wave sleep. The means for causing is configured to cause the means for providing sensory stimuli to decrease the intensity of, and/or cease providing, the sensory stimulation to the subject during a given period of slow wave sleep responsive to an arousal level determined by the means for determining the current sleep stage breaching an arousal level threshold during the given period of slow wave sleep

These and other objects, features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic illustration of a system configured to manage a current sleep session of a subject.

<figref idref="DRAWINGS">FIG. 2</figref> illustrates experimental data from six subjects showing slow wave activity versus acoustic stimulation volume level.

<figref idref="DRAWINGS">FIG. 3</figref> illustrates a headset worn by a subject and includes sensing electrodes, a bio-signal amplifier, and a wireless audio device.

<figref idref="DRAWINGS">FIG. 4</figref> illustrates acoustic stimulation delivered to a subject in the form of auditory tones.

<figref idref="DRAWINGS">FIG. 5</figref> illustrates a method for managing a current sleep session of a subject with a management system.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein, “directly coupled” means that two elements are directly in contact with each other. As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other.

As used herein, the word “unitary” means a component is created as a single piece or unit. That is, a component that includes pieces that are created separately and then coupled together as a unit is not a “unitary” component or body. As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).

Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic illustration of a system <b>10</b> configured to manage a current sleep session of a subject <b>12</b>. In some embodiments, system <b>10</b> may comprise one or more of a sensory stimulator <b>16</b>, a sensor <b>18</b>, a processor <b>20</b>, electronic storage <b>22</b>, a user interface <b>24</b>, and/or other components. System <b>10</b> is configured such that a current sleep stage of subject <b>12</b> is determined one or more times during the sleep session. System <b>10</b> is configured to provide sensory stimuli to subject <b>12</b> during the current sleep session based on output signals generated by sensor <b>18</b>. System <b>10</b> is configured such that the delivery of sensory stimulation during the current sleep session induces sleep slow waves and/or adjusts (e.g. enhance and/or decrease) slow wave activity (SWA) in subject <b>12</b>. The manifestation of induced sleep slow waves may be measured through SWA. The delivery of the sensory stimulation is timed to correspond to sleep stages associated with SWA.

Sleep stages may include rapid eye movement (REM) sleep, and/or non-rapid eye movement (NREM) stage N<b>1</b>, stage N<b>2</b>, and/or stage N<b>3</b> sleep. In some embodiments, stage N<b>3</b> sleep may be and/or correspond to slow wave sleep. In some embodiments, stage N<b>2</b> and/or stage N<b>3</b> sleep may be slow wave sleep. In some embodiments, slow waves may not be present throughout the whole N<b>3</b> period, for example, but it may be significantly more likely that such slow waves are present during N<b>3</b>. Slow waves may also be present (although to a lesser extent) during N<b>2</b>, for example.

Slow wave sleep and/or SWA may be observed and/or estimated by way of an electroencephalogram (EEG). In some embodiments, SWA corresponds to the power of the EEG signal in the 0.5-4.0 Hz band. In some embodiments, this band is set to 0.5-4.5 Hz. SWA has a typical behavior throughout cyclic variations of a given sleep session. SWA increases during NREM sleep, declines before the onset of REM sleep, and remains low during REM sleep. SWA in successive NREM (e.g., slow wave sleep) episodes progressively decreases from one episode to the next.

Higher intensity sensory stimulation results in a higher level of SWA. For example, <figref idref="DRAWINGS">FIG. 2</figref> illustrates experimental data from six subjects (S<b>1</b>-S<b>6</b>) showing SWA <b>200</b> versus acoustic stimulation volume level <b>202</b>. The trend lines <b>204</b>-<b>214</b> show increasing SWA in each subject with increasing acoustic stimulation volume. However, starting the sensory stimulation at a high level risks waking the subjects. The system described herein is configured to incrementally increase the intensity of the sensory stimulation without waking subject <b>12</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref>) from sleep.

Returning to <figref idref="DRAWINGS">FIG. 1</figref>, system <b>10</b> is configured to provide the sensory stimuli at a first intensity level, determine the effectiveness of the provided sensory stimuli, and increase the intensity level of the sensory stimuli based on the determined effectiveness. The effectiveness determination and the corresponding intensity increase are repeated one or more times during a given slow wave sleep episode. In some embodiments, system <b>10</b> is configured to continue the effectiveness determinations and the corresponding intensity increases during the given slow wave sleep episode until the intensity level reaches a maximum level. In some embodiments, system <b>10</b> is configured to continue the effectiveness determinations and the corresponding intensity increases during the given slow wave sleep episode until an arousal level of subject <b>12</b> breaches an arousal level threshold during the given period of slow wave sleep. In some embodiments, responsive to the intensity reaching the maximum level, system <b>10</b> is configured such that the intensity of the stimulation is no longer increased. In some embodiments, responsive to the arousal level breaching the arousal level threshold, system <b>10</b> is configured to cease providing the sensory stimuli to subject <b>12</b>. In some embodiments, responsive to the intensity reaching the maximum level and/or the arousal level breaching the arousal level threshold, system <b>10</b> is configured to decrease the intensity of the sensory stimuli provided to subject <b>12</b>.

In <figref idref="DRAWINGS">FIG. 1</figref>, sensory stimulator <b>16</b>, sensor <b>18</b>, processor <b>20</b>, electronic storage <b>22</b>, and user interface <b>24</b> are shown as separate entities. This is not intended to be limiting. Some and/or all of the components of system <b>10</b> and/or other components may be grouped into one or more singular devices. For example, <figref idref="DRAWINGS">FIG. 3</figref> illustrates a headset <b>300</b> worn by a subject <b>302</b> and includes sensing electrodes <b>304</b>, a bio-signal amplifier <b>306</b>, and a wireless audio device <b>308</b>. Sensing electrodes <b>304</b> and bio-signal amplifier <b>306</b> may be represented, for example, by sensor <b>18</b> in <figref idref="DRAWINGS">FIG. 1</figref>. Wireless audio device <b>308</b> may be represented, for example, by sensory stimulator <b>16</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>.

Returning to <figref idref="DRAWINGS">FIG. 1</figref>, sensory stimulator <b>16</b> is configured to provide sensory stimuli to subject <b>12</b>. Sensory stimulator <b>16</b> is configured to provide sensory stimuli to subject <b>12</b> prior to the current sleep session, during the current sleep session, and/or at other times. For example, sensory stimulator <b>16</b> may be configured to provide sensory stimuli to subject <b>12</b> during slow wave sleep in the current sleep session. Sensory stimulator <b>16</b> may be configured to provide sensory stimuli to subject <b>12</b> during the current sleep session to induce sleep slow waves and/or adjust SWA in subject <b>12</b>. In some embodiments, sensory stimulator <b>16</b> may be configured such that adjusting includes increasing (e.g., enhancing), decreasing, and/or other adjustment of SWA in subject <b>12</b>.

In some embodiments, sensory stimulator <b>16</b> may be configured to induce sleep slow waves and/or adjust SWA through non-invasive brain stimulation and/or other methods. Sensory stimulator <b>16</b> may be configured to induce sleep slow waves and/or adjust SWA through non-invasive brain stimulation using the sensory stimuli. The sensory stimuli include odors, sounds, visual stimulation, touches, tastes, and/or other stimuli. For example, transcranial magnetic stimulation may be applied to subject <b>12</b> to trigger, increase, and/or decrease SWA. As another example, sensory stimulator <b>16</b> may be configured to induce sleep slow waves and/or adjust SWA via auditory stimulation of subject <b>12</b>. Examples of sensory stimulator <b>16</b> may include one or more of a music player, a tone generator, a collection of electrodes on the scalp of subject <b>12</b>, a unit to deliver vibratory stimulation (also known as somato-sensory stimulation), a coil generating a magnetic field to directly stimulate the brain's cortex, light generators, a fragrance dispenser, and/or other devices.

In some embodiments, sensory stimulator <b>16</b> is configured to generate the sensory stimuli at one or more intensities. For example, sensory stimulator <b>16</b> may generate tones at a first lower decibel level and/or a second higher decibel level. In some embodiments, the one or more intensities may include the same sensory stimuli delivered at different timing intervals. For example, sensory stimulator <b>16</b> may generate tones at the first lower decibel level at a first lower frequency interval (first intensity level) and/or at a second higher frequency interval (second intensity level).

Sensor <b>18</b> is configured to generate output signals conveying information related to a current sleep stage of subject <b>12</b>. Sensor <b>18</b> may comprise one or more sensors that measure such parameters directly. For example, sensor <b>18</b> may include electrodes configured to detect electrical activity along the scalp of subject <b>12</b> resulting from current flows within the brain of subject <b>12</b>. Sensor <b>18</b> may comprise one or more sensors that generate output signals conveying information related to a current sleep stage of the subject indirectly. For example, one or more sensors <b>18</b> may generate an output based on a heart rate of subject <b>12</b> (e.g., sensor <b>18</b> may be a heart rate sensor located on the chest of subject <b>12</b>, and/or be configured as an optical sensor included in a bracelet on a wrist of subject <b>12</b>, and/or be located on another limb of subject <b>12</b>), movement of subject <b>12</b> (e.g., sensor <b>18</b> may include a bracelet around the wrist and/or ankle of subject <b>12</b> with an accelerometer such that sleep may be analyzed using actigraphy signals), changes in skin color of subject <b>12</b> (e.g., sensor <b>18</b> may include a camera that can detect changes is skin color of subject <b>12</b> and infer vital signs such as heart rate, breathing rate, and/or other vital signs from the changes in color), respiration of subject <b>12</b>, and/or other characteristics of subject <b>12</b>. Although sensor <b>18</b> is illustrated at a single location in communication with subject <b>12</b>, this is not intended to be limiting. Sensor <b>18</b> may include sensors disposed in a plurality of locations, such as for example, within (or in communication with) sensory stimulator <b>16</b>, and/or in other locations.

Processor <b>20</b> is configured to provide information processing capabilities in system <b>10</b>. As such, processor <b>20</b> may comprise one or more of a digital processor, an analog processor, and a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information. Although processor <b>20</b> is shown in <figref idref="DRAWINGS">FIG. 1</figref> as a single entity, this is for illustrative purposes only. In some implementations, processor <b>20</b> may comprise a plurality of processing units. These processing units may be physically located within the same device (e.g., sensory stimulator <b>16</b>), or processor <b>20</b> may represent processing functionality of a plurality of devices operating in coordination.

As shown in <figref idref="DRAWINGS">FIG. 1</figref>, processor <b>20</b> is configured to execute one or more computer program modules. The one or more computer program modules may comprise one or more of a sleep stage module <b>32</b>, a slow wave sleep timing module <b>33</b>, a control module <b>34</b>, an effectiveness module <b>36</b>, an adjustment module <b>38</b>, and/or other modules. Processor <b>20</b> may be configured to execute modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and/or <b>38</b> by software; hardware; firmware; some combination of software, hardware, and/or firmware; and/or other mechanisms for configuring processing capabilities on processor <b>20</b>.

It should be appreciated that although modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and <b>38</b> are illustrated in <figref idref="DRAWINGS">FIG. 1</figref> as being co-located within a single processing unit, in implementations in which processor <b>20</b> comprises multiple processing units, one or more of modules <b>32</b>, <b>33</b>, <b>34</b>, <b>26</b>, and/or <b>38</b> may be located remotely from the other modules. The description of the functionality provided by the different modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and/or <b>38</b> described below is for illustrative purposes, and is not intended to be limiting, as any of modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and/or <b>38</b> may provide more or less functionality than is described. For example, one or more of modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and/or <b>38</b> may be eliminated, and some or all of its functionality may be provided by other modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and/or <b>38</b>. As another example, processor <b>20</b> may be configured to execute one or more additional modules that may perform some or all of the functionality attributed below to one of modules <b>32</b>, <b>33</b>, <b>34</b>, <b>36</b>, and/or <b>38</b>.

Sleep stage module <b>32</b> is configured to determine the current sleep stage of subject <b>12</b> based on the output signals of sensor <b>18</b>. As described above, the current sleep stage of subject <b>12</b> may correspond to one or more of wakefulness, REM sleep, stage N<b>1</b>, stage N<b>2</b>, and/or stage N<b>3</b> sleep. Sleep stage module <b>32</b> is configured to determine whether subject <b>12</b> is presently in slow wave sleep. In some embodiments, slow wave sleep and/or slow wave activity may correspond to stage N<b>3</b> sleep. In some embodiments, stage N<b>2</b> and/or stage N<b>3</b> sleep may be slow wave sleep and/or correspond to slow wave activity.

In some embodiments, sleep stage module <b>32</b> may determine the current sleep stage of subject <b>12</b> based on an analysis of the information conveyed by the output signals of sensor <b>18</b>. The analysis may include generating and/or monitoring an EEG during the sleep session of subject <b>12</b>. In some embodiments, the analysis may include detecting slow wave sleep based on a power in a delta band and/or a power in a beta band of the EEG. The power in the delta band is usually defined as the power in the frequency range 0.5-4.5 Hz although there is no standard definition of the frequency limits. The power in the beta band is usually defined as the power in the frequency range 15-30 Hz although variations in limits of the range are very common.

In some embodiments, sleep stage module <b>32</b> is configured to determine one or more arousal levels of the subject during the current sleep session. The one or more arousal levels may indicate a level of wakefulness in subject <b>12</b>. The one or more arousal levels may be determined based on the output signals of sensor <b>18</b>, information stored in electronic storage <b>22</b>, testing performed prior to the current sleep session, information received and/or selected via user interface <b>24</b>, and/or other information. In some embodiments, the one or more arousal levels may be determined based on the analysis of the information related to the EEG. For example, the likelihood for an arousal may be quantified from the EEG power in the beta band in short temporal windows (typically about 1.5 second long, for example). Responsive to the power in the beta band exceeding a predefined threshold, system <b>10</b> may decide that an arousal is present. In some embodiments, the beta band power threshold for arousals may be determined based on a previous sleep session of subject <b>12</b>, based on information related a population of subjects demographically similar to subject <b>12</b>, and/or based on other information. For example, the beta band power threshold may be determined based on a calibration night of sleep during which the EEG of subject <b>12</b> is measured and the statistics of the beta power throughout the sleep session are analyzed to set the threshold. As another example, the beta band power threshold may be determined via a database containing the beta thresholds for a population of subjects. The beta band power threshold for subject <b>12</b> may be determined based on demographically matching subject <b>12</b> with subjects present in the database.

Slow wave sleep timing module <b>33</b> is configured to determine individual time periods of slow wave sleep in subject <b>12</b> during the current sleep session. Slow wave sleep timing module <b>33</b> is configured to determine the individual time periods of slow wave sleep based on the sleep stage determinations (e.g., whether subject <b>12</b> is presently in slow wave sleep) by sleep stage module <b>32</b>. For example, slow wave sleep timing module <b>33</b> may determine a first individual time period of slow wave sleep such that the start of the first individual time period coincides with the start of a first slow wave sleep episode during the current sleep session and/or stops with the end of the first slow wave sleep episode (e.g., sleep stage module <b>32</b> determines that subject <b>12</b> is no longer in slow wave sleep). The start of a second individual time period of slow wave sleep may coincide with the start of a second episode of slow wave sleep during the current sleep session and/or stops with the end of the second slow wave sleep episode.

In some embodiments, slow wave sleep timing module <b>33</b> is configured to determine the individual time periods such that the individual time periods begin a predetermined amount of time after sleep stage module <b>32</b> determines that subject <b>12</b> is presently in slow wave sleep. In some embodiments, slow wave sleep timing module <b>33</b> is configured to determine the individual time periods such that the individual time periods end a predetermined amount of time after sleep stage module <b>32</b> determines that subject <b>12</b> is presently in slow wave sleep. In some embodiments, the one or more predetermined amounts of time may be based on typical amounts of time between the beginning of slow wave sleep and the end of a slow wave sleep for a given episode of slow wave sleep during the current sleep session. The typical amounts of time may be determined based on a current sleep session of subject <b>12</b>, previous sleep sessions of subject <b>12</b>, and/or other sleep sessions. In some embodiments, the one or more predetermined amounts of time may be programmed at manufacture, set by a user via user interface <b>24</b>, and/or determined by other methods.

In some embodiments, sleep stage module <b>32</b> may determine the one or more arousal levels during the individual time periods of slow wave sleep. In some embodiments, slow wave sleep timing module <b>33</b> may determine the end of a given individual time period of slow wave sleep based on the arousal levels determined by sleep stage module <b>32</b>.

Control module <b>34</b> is configured to control sensory stimulator <b>16</b> to provide the sensory stimuli to subject <b>12</b> during the individual time periods of slow wave sleep (e.g., during stage N<b>3</b> sleep). In some embodiments, the timing for delivery of sensory stimulation may correspond to the determination that subject <b>12</b> is presently in slow wave sleep. Control module <b>34</b> may be configured to control sensory stimulator <b>16</b> to provide the sensory stimuli to subject <b>12</b> such that the provided sensory stimuli corresponds to sleep stages associated with slow wave activity because the likelihood for slow-wave induction, and/or adjustment during the specific sleep stage may be comparatively higher than in other sleep stages, the user may be less likely to be awakened by the sensory stimuli, and/or for other reasons.

In some embodiments, control module <b>34</b> is configured to control sensory stimulator <b>16</b> to provide the sensory stimuli in the form of auditory tones that are brief in duration (e.g., about 50 ms long), have a predetermined frequency, and are separated from each other by an inter-tone-interval. In some embodiments, one or more of the auditory tone duration, the predetermined frequency, the inter-tone-interval, and/or other characteristics of the sensory stimuli may be programmed at manufacture, set by a user via user interface <b>24</b>, determined by system <b>10</b> based on previous sleep sessions of subject <b>12</b>, determined based on the current sleep session, and/or determined by other methods.

In some embodiments, control module <b>34</b> is configured to control sensory stimulator <b>16</b> to provide the sensory stimuli (e.g., auditory tones) to subject <b>12</b> such that habituation in subject <b>12</b> is avoided. Habituation is a decrease of a response (e.g., behavioral and/or cortical) to a repeated eliciting stimulus not due to fatigue. Habituation to repetitive sensory stimuli manifests itself as a reduction in amplitude of the cortical response as determined via the EEG. Habituation may adversely affect SWA induction, and/or adjustment (e.g., enhancement) caused by system <b>10</b>. Control module <b>34</b> may be configured to randomize the frequency of the sensory stimuli to counter habituation.

Control module <b>34</b> is configured to control sensory stimulator <b>16</b> to provide the sensory stimuli at a first intensity level during the first individual time period of slow wave sleep. Control module <b>34</b> may be configured to control sensory stimulator <b>16</b> to increase the intensity of the sensory stimuli to the first intensity level relative to a baseline intensity level. The baseline intensity level may be the intensity level of ambient sensory stimuli in a room where the subject is sleeping (e.g. noise from automobile traffic outside the room, lighting, etc.). In some embodiments, control module <b>34</b> may control sensory stimulator <b>16</b> to provide sensory stimuli at a baseline intensity level. The baseline intensity level may be zero intensity (e.g., no sensory stimulation is provided by sensory stimulator <b>16</b>) and/or may be an amount of sensory stimulation determined based on the current and/or previous sleep sessions of the subject, and/or other information, for example.

Control module <b>34</b> is configured to control sensory stimulator <b>16</b> to provide the sensory stimuli at the first intensity level such that the sensory stimulation does not wake subject <b>12</b>. Control module <b>34</b> is configured such that the first intensity level is determined based on previous sleep sessions of subject <b>12</b>, testing performed on subject <b>12</b> during wakefulness, and/or other information. In some embodiments, the first intensity level may be the lowest intensity subject <b>12</b> is able to perceive during wakefulness, for example. Information related to the intensity of stimulation during previous sleep sessions of subject <b>12</b> and/or testing performed on subject <b>12</b> during wakefulness may be stored in electronic storage <b>22</b>, for example. In some embodiments, control module <b>34</b> may cause information related to the current sleep session of subject <b>12</b> to be stored in electronic storage <b>22</b>. Information related to the current sleep session may include information related to the intensity level of the sensory stimulation, sleep stage information, timing information, and/or other information.

Effectiveness module <b>36</b> is configured to determine an effectiveness of the provided sensory stimuli. The effectiveness is related to an increase in SWA caused by the provided sensory stimuli. The effectiveness is determined based on the output signals of sensor <b>18</b>, information related to the EEG of subject <b>12</b> during the current sleep session, and/or other information. For example, effectiveness module <b>36</b> is configured to determine a first effectiveness of the sensory stimuli provided at the first intensity level during the first individual time period. In some embodiments, effectiveness module <b>36</b> is configured to determine the effectiveness of the provided sensory stimuli based on the SWA in subject <b>12</b> during a window of time just after the sensory stimulation is delivered to subject <b>12</b> at the first intensity level by sensory stimulator <b>16</b>. In some embodiments, the effectiveness is determined by comparing the SWA in a window of time just before the stimulation to the SWA in a window of time just after the stimulation.

Adjustment module <b>38</b> is configured to cause sensory stimulator <b>16</b> to increase the intensity of the provided sensory stimuli based on the intensity of sensory stimuli previously provided to subject <b>12</b>, the determined effectiveness, the EEG power in the spindle band (e.g., 11-15 Hz), a prediction of the effectiveness, and/or other information. For example, adjustment module <b>38</b> may cause the intensity of the provided sensory stimuli to increase to a second intensity level based on the first effectiveness. Adjustment module <b>38</b> may be configured such that an increase in the intensity of sensory stimulation is based on information determined via the EEG (e.g., by sleep stage module <b>32</b>). In some embodiments, adjustment module <b>38</b> is configured such that an increase in the intensity of sensory stimulation is based on information determined by adjustment module <b>38</b> via an algorithm. Algorithm inputs may include the determined effectiveness, information related to a predicted SWA enhancement determined via information related to the EEG, information related to a spindle rate/density determined via the EEG, and/or other information. In some embodiments, the EEG power in the spindle band (e.g., about 11 to 15 Hz) may be used to detect sleep spindles and estimate the spindle rate/density (spindles/minute). A higher spindle rate/density indicates a higher arousal threshold in relation to external stimulation. If the spindle rate/density is high, then the increase in the stimulation intensity may be larger than it would be if the spindle rate/density were low. In some embodiments, a prediction of the effectiveness may be obtained by adjustment module <b>38</b> via fitting a curve to the sleep slow waves and extrapolating the result to the time instants where the stimulation is delivered.

In some embodiments, effectiveness module <b>36</b> and/or adjustment module <b>38</b> are configured to repeat the effectiveness determination and the intensity increase one or more times during the individual time periods of slow wave sleep such that the intensity level of the sensory stimulation is incrementally increased during the individual time periods of slow wave sleep. Effectiveness module <b>36</b> and/or adjustment module <b>38</b> are configured to repeat the effectiveness determination and the intensity increase one or more times until expiration of the individual time periods. For example, effectiveness module <b>36</b> may determine a second effectiveness of the sensory stimuli provided at the second intensity level during the first individual time period of slow wave sleep and adjustment module <b>38</b> may cause sensory stimulator <b>16</b> to increase the intensity of the provided sensory stimuli to a third intensity level.

In some embodiments, adjustment module <b>38</b> is configured to cause sensory stimulator <b>16</b> to increase the intensity level one or more times during a given time period of slow wave sleep until the intensity level reaches a maximum level. In some embodiments, the maximum intensity level may be obtained by adjustment module <b>38</b> responsive to testing performed on subject <b>12</b> during wakefulness prior to the current sleep session. In some embodiments, the maximum intensity level may be obtained by adjustment module <b>38</b> responsive to user interface <b>24</b> receiving entry and/or selection of information related to the maximum intensity level. In some embodiments, adjustment module <b>38</b> is configured to determine the maximum intensity level based on the current sleep session of subject <b>12</b> and/or previous sleep sessions of subject <b>12</b>.

In some embodiments, adjustment module <b>38</b> is configured to cause sensory stimulator <b>16</b> to cease providing the sensory stimuli to subject <b>12</b> during a given period of slow wave sleep responsive to an arousal level determined by sleep stage module <b>32</b> breaching an arousal level threshold during the given period of slow wave sleep. In some embodiments, adjustment module <b>38</b> is configured to cause sensory stimulator <b>16</b> to decrease the intensity of the sensory stimuli provided to subject <b>12</b> responsive to the arousal level of the subject breaching the arousal level threshold.

The arousal level threshold may be determined by sleep stage module <b>32</b> based on information related to the current sleep session, information related to a previous sleep session, and/or other information. In some embodiments, the arousal level threshold may be obtained by sleep stage module <b>32</b> responsive to testing performed on subject <b>12</b> during wakefulness prior to the current sleep session. In some embodiments, the arousal level threshold may be determined by sleep stage module <b>32</b> responsive to user interface <b>24</b> receiving entry and/or selection of information related to the arousal level threshold.

In some embodiments, incrementally increasing the intensity level of the sensory stimulation may increase the arousal level threshold for subject <b>12</b>. For example, an arousal level threshold determined for auditory stimulation of subject <b>12</b> during testing prior to the current sleep session may indicate that subject <b>12</b> wakes from sleep responsive to sound at a first decibel level. Subject <b>12</b> may wake from sleep at a second higher decibel level during the current sleep session responsive to the intensity of the sensory stimulation being incrementally increased by system <b>10</b> during the current sleep session as described herein.

<figref idref="DRAWINGS">FIG. 4</figref> illustrates acoustic stimulation delivered to a subject in the form of auditory tones <b>400</b> (e.g. by sensory stimulator <b>16</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>). <figref idref="DRAWINGS">FIG. 4</figref> illustrates an example of at least some of the functionality of sensory stimulator <b>16</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref>), sleep stage module <b>32</b> (<figref idref="DRAWINGS">FIG. 1</figref>), slow wave sleep timing module <b>33</b> (<figref idref="DRAWINGS">FIG. 1</figref>), control module <b>34</b> (<figref idref="DRAWINGS">FIG. 1</figref>), effectiveness module <b>36</b> (<figref idref="DRAWINGS">FIG. 1</figref>), adjustment module <b>38</b> (<figref idref="DRAWINGS">FIG. 1</figref>), and/or other components of system <b>10</b>. The volume (intensity) <b>402</b> of the acoustic tones is incrementally increased <b>404</b> (<figref idref="DRAWINGS">FIG. 4A</figref>) based on the effectiveness of previous tones at enhancing SWA in the subject. The tones may have a duration, a frequency, an inter-tone-interval, and/or other characteristics. The tones may be generated for the subject while the subject is sleeping in an environment having a baseline volume, V_B. The baseline volume level may be the ambient volume in a room where the subject is sleeping, for example. In some embodiments, control module <b>34</b> may control sensory stimulator <b>16</b> to provide noise at a baseline volume level. The baseline volume level may be zero volume, may be determined based on the current and/or previous sleep sessions of the subject, and/or include other volumes.

The volume of the first tone (e.g., determined by control module <b>34</b>), V₀(<figref idref="DRAWINGS">FIG. 4B</figref>), may be determined based on previous sleep sessions of subject <b>12</b>, testing performed on subject <b>12</b> during wakefulness, and/or other information. In some embodiments, the first tone volume may be the lowest volume the subject is able to hear during wakefulness, for example. The first incremental increase, Δ₀, may be equal to V₀−V_B, for example.

The volume of the k-th tone (<figref idref="DRAWINGS">FIG. 4C</figref>), V_k, may be determined (e.g., by adjustment module <b>38</b>) based on the volume of the previous tone using V_k=V_k−1+Δ_k, where Δ_kis the incremental increase at the k-th tone. The incremental increase, Δ_k, may be determined based on the estimated effectiveness (e.g., determined by effectiveness module <b>36</b>) in enhancing SWA after delivering the (k−1)-th tone, information related to an EEG of the subject (e.g., determined by sleep stage module <b>32</b>), and/or other information. For example, the incremental increase may be determined based on the equation Δ_k(E_SWA, P_SWA, σ_r), where E_SWAis an estimated effectiveness in enhancing SWA in the subject after the k-th tone has been delivered, P_SWAis a prediction of the SWA enhancement following the k-th tone, and σ_ris a spindle rate.

The estimated effectiveness in enhancing SWA after the k-th tone has been delivered, E_SWA, may be, for example, a ratio between the SWA in a time window lasting for T seconds between the time instants t_k+τ−T and t_k+τ (where t_kis the time at which the k-th tone was delivered and τ&gt;0) and the SWA in a time window lasting for 2T seconds between the time instants t_k+τ−3T and t_k+τ−T. In some embodiments, T is a constant having a value of about 500 milliseconds, for example, and τ is a constant having a value of about 200 milliseconds, for example. Because τ seconds are considered after delivery of the k-th tone, the influence of this stimulation may be taken into account to determine the effectiveness of the SWA enhancement. The values given here for T and τ are not intended to be limiting. T and/or τ may have and/or be assigned values such that the influence of the current stimulation (delivered at t_k) is taken into account.

The prediction of the SWA enhancement following the k-th tone, P_SWA, may be determined based on tracking the induced sleep slow waves using a phase-locked-loop (PLL) approach, for example, and predicting the phase of the future sleep slow waves. Based on the PLL approach, system <b>10</b> may be configured such that a sinusoidal curve at a frequency of 1 Hz, for example, is fit to the sleep slow waves. Sleep stage module <b>32</b>, control module <b>34</b>, effectiveness module <b>36</b> and/or adjustment module <b>38</b> may be configured such that the fit is performed in real-time. Based on the fit, system <b>10</b> may predict when (with respect to the sleep slow wave) the acoustic tone is to be delivered. For example, system <b>10</b> may be configured such that the acoustic tone is delivered in the vicinity of the negative peak of the sleep slow wave.

The spindle rate, σ_r, may be determined based on a sleep spindle that is determined via the EEG. The sleep spindle is a thalamocortical rhythm manifested on the EEG as a brief 11-15 Hz oscillation and is thought to be capable of modulating the influence of external stimuli. The robustness of sleep in the face of acoustic stimulation may be predicted from the spindle rate. A higher spindle rate/density indicates a higher robustness of sleep is in the presence of acoustic stimulation. The spindle rate may be considered high responsive to the spindle rate exceeding 5 spindles per minute, for example. In the case of a high spindle rate, the incremental increase, Δ_k, may be increased by about 20% from the previous intensity, for example.

As shown in <figref idref="DRAWINGS">FIG. 4D</figref>, responsive to an arousal level of the subject (e.g., determined by sleep stage module <b>32</b>) breaching (e.g., determined by adjustment module <b>38</b>) an arousal level threshold (e.g., determined by sleep stage module <b>32</b>), the sensory stimulation is stopped and the volume is reset to the baseline level (e.g., by adjustment module <b>38</b>). Responsive to the subject entering a subsequent time period of slow wave sleep (e.g., determined by slow wave sleep timing module <b>33</b>), the process of incrementally increasing the intensity of the sensory stimulation restarts.

Returning to <figref idref="DRAWINGS">FIG. 1</figref>, electronic storage <b>22</b> comprises electronic storage media that electronically stores information. The electronic storage media of electronic storage <b>22</b> may comprise one or both of system storage that is provided integrally (i.e., substantially non-removable) with system <b>10</b> and/or removable storage that is removably connectable to system <b>10</b> via, for example, a port (e.g., a USB port, a firewire port, etc.) or a drive (e.g., a disk drive, etc.). Electronic storage <b>22</b> may comprise one or more of optically readable storage media (e.g., optical disks, etc.), magnetically readable storage media (e.g., magnetic tape, magnetic hard drive, floppy drive, etc.), electrical charge-based storage media (e.g., EPROM, RAM, etc.), solid-state storage media (e.g., flash drive, etc.), and/or other electronically readable storage media. Electronic storage <b>22</b> may store software algorithms, information determined by processor <b>20</b>, information received from subject <b>12</b>, and/or other information that enables system <b>10</b> to function properly. For example, electronic storage <b>22</b> may store information related to the intensity levels of the sensory stimulation provided to subject <b>12</b> during previous sleep sessions and/or the current sleep session. Electronic storage <b>22</b> may be (in whole or in part) a separate component within system <b>10</b>, or electronic storage <b>22</b> may be provided (in whole or in part) integrally with one or more other components of system <b>10</b> (e.g., processor <b>20</b>).

User interface <b>24</b> is configured to provide an interface between system <b>10</b> and subject <b>12</b>, and/or other users through which subject <b>12</b> and/or the other users may provide information to and receive information from system <b>10</b>. Other users may include doctors, caregivers, and/or other users. This enables data, cues, results, and/or instructions and any other communicable items, collectively referred to as “information,” to be communicated between a user (e.g., subject <b>12</b>) and one or more of sensory stimulator <b>16</b>, sensor <b>18</b>, processor <b>20</b>, and/or other components of system <b>10</b>. For example, an EEG may be displayed to a caregiver via user interface <b>24</b>.

Examples of interface devices suitable for inclusion in user interface <b>24</b> comprise a keypad, buttons, switches, a keyboard, knobs, levers, a display screen, a touch screen, speakers, a microphone, an indicator light, an audible alarm, a printer, a tactile feedback device, and/or other interface devices. In some embodiments, user interface <b>24</b> comprises a plurality of separate interfaces. In some embodiments, user interface <b>24</b> comprises at least one interface that is provided integrally with sensory stimulator <b>16</b> and/or other components of system <b>10</b>.

It is to be understood that other communication techniques, either hard-wired or wireless, are also contemplated by the present disclosure as user interface <b>24</b>. For example, the present disclosure contemplates that user interface <b>24</b> may be integrated with a removable storage interface provided by electronic storage <b>22</b>. In this example, information may be loaded into system <b>10</b> from removable storage (e.g., a smart card, a flash drive, a removable disk, etc.) that enables the user(s) to customize the implementation of system <b>10</b>. Other exemplary input devices and techniques adapted for use with system <b>10</b> as user interface <b>24</b> comprise, but are not limited to, an RS-232 port, RF link, an IR link, modem (telephone, cable or other). In short, any technique for communicating information with system <b>10</b> is contemplated by the present disclosure as user interface <b>24</b>.

<figref idref="DRAWINGS">FIG. 5</figref> illustrates a method <b>500</b> for managing a current sleep session of a subject with a management system. The system comprises one or more sensory stimulators, one or more sensors, and one or more processors configured to execute computer program modules. The computer program modules comprise a sleep stage module, a slow wave sleep timing module, a control module, an effectiveness module, and an adjustment module. The operations of method <b>500</b> presented below are intended to be illustrative. In some embodiments, method <b>500</b> may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of method <b>500</b> are illustrated in <figref idref="DRAWINGS">FIG. 5</figref> and described below is not intended to be limiting.

In some embodiments, method <b>500</b> may be implemented in one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices executing some or all of the operations of method <b>500</b> in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and/or software to be specifically designed for execution of one or more of the operations of method <b>500</b>.

At an operation <b>502</b>, output signals conveying information related to a current sleep stage of the subject during the current sleep session are generated. In some embodiments, operation <b>502</b> is performed by one or more sensors the same as or similar to sensors <b>18</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>504</b>, the current sleep stage of the subject is determined based on the output signals. In some embodiments, operation <b>504</b> is performed by a computer program module the same as or similar to sleep stage module <b>32</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>506</b>, whether the subject is presently in slow wave sleep is determined. Whether the subject is presently in slow wave sleep is determined based on the sleep stage determinations. In some embodiments, slow wave sleep may be stage N<b>3</b> sleep. In some embodiments, operation <b>506</b> is performed by a computer program module the same as or similar to sleep stage module <b>32</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>508</b>, individual time periods of slow wave sleep during the current sleep session are determined. The individual time periods of slow wave sleep are determined based on the sleep stage determinations. In some embodiments, operation <b>508</b> is performed by a computer program module the same as or similar to slow wave sleep timing module <b>33</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>510</b>, the one or more sensory stimulators are controlled to provide sensory stimuli to the subject during the individual time periods of slow wave sleep. The controlling includes controlling the one or more sensory stimulators to provide the sensory stimuli at a first intensity level during a first individual time period of slow wave sleep. In some embodiments, the first intensity level may be determined based on previous sleep sessions of the subject. In some embodiments, operation <b>510</b> is performed by a computer program module the same as or similar to control module <b>34</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>512</b>, an effectiveness of the provided sensory stimuli is determined. The effectiveness is related to an increase in slow wave activity caused by the sensory stimuli. The effectiveness is determined based on the output signals. A first effectiveness of the sensory stimuli provided at the first intensity level during the first individual time period is determined. In some embodiments, operation <b>512</b> is performed by a computer program module the same as or similar to effectiveness module <b>36</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>514</b>, the one or more sensory stimulators are caused to increase the intensity of the provided sensory stimuli. The increase is based on the determined effectiveness. The intensity of the provided sensory stimuli is increased to a second intensity level based on the first effectiveness, and/or other information. In some embodiments, the increase in the intensity of sensory stimulation is based on information determined via an algorithm. Algorithm inputs may include the determined effectiveness, information related to a predicted SWA enhancement determined via information related to the EEG, information related to a spindle rate/density determined via the EEG, and/or other information. In some embodiments, the EEG power in the spindle band (e.g., about 11 to 15 Hz) may be used to detect sleep spindles and estimate the spindle rate/density (spindles/minute). A higher spindle rate/density indicates a higher arousal threshold in relation to external stimulation. If the spindle rate/density is high, then the increase in the stimulation intensity may be larger than it would be if the spindle rate/density were low. In some embodiments, a prediction of the effectiveness may be obtained via fitting a curve to the sleep slow waves and extrapolating the result to the time instants where the stimulation is delivered. In some embodiments, operation <b>514</b> is performed by a computer program module the same as or similar to adjustment module <b>38</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

At an operation <b>516</b>, the effectiveness determination and then the intensity increase are repeated one or more times during the individual time periods of slow wave sleep. The effectiveness determination and the intensity increase are repeated one or more times until expiration of the individual time periods. For example, a second effectiveness of the sensory stimuli provided at the second intensity level during the first individual time period of slow wave sleep is determined and the one or more sensory stimulators are caused to increase the intensity of the provided sensory stimuli to a third intensity level. In some embodiments, the intensity level may be increased one or more times until the intensity reaches a maximum level. In some embodiments, the sensory stimulators may be caused to cease providing the sensory stimuli during a given period of slow wave sleep responsive to an arousal level of the subject breaching an arousal level threshold during the given period of slow wave sleep. In some embodiments, the sensory stimulators may be caused to decrease the intensity of the sensory stimulation during a given period of slow wave sleep responsive to the arousal level of the subject breaching the arousal level threshold during the given period of slow wave sleep. In some embodiments, operation <b>516</b> is performed by computer program modules the same as or similar to sleep stage module <b>32</b>, effectiveness module <b>36</b>, and/or adjustment module <b>38</b> (shown in <figref idref="DRAWINGS">FIG. 1</figref> and described herein).

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” or “including” does not exclude the presence of elements or steps other than those listed in a claim. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. In any device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain elements are recited in mutually different dependent claims does not indicate that these elements cannot be used in combination.

Although the description provided above provides detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the disclosure is not limited to the expressly disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.